1. Field of the Invention
This invention relates to pneumatic automobile tires, more particularly such a tire which has a carcass reinforced with monofilament cords.
Generally, pneumatic tires for use on automotive vehicles incorporate reinforcing cords made of metallic or fibrous materials. Fibrous tire cords are typically fabricated by twisting multifilaments of nylon, polyester and other organic polymers to a desired strand and have found wide use as they have an advantage over metallic tire cords particularly in terms of weight.
It has recently been proposed to use monofilaments in place of multifilaments in view of their higher rigidity. However, monofilaments of round cross section are found less resistant to fatigue. This problem is reportedly overcome by using cross-sectionally flat monofilaments such as of an elongate rectangular configulation shown in FIG. 7 of the accompanying drawings. Such flat monofilaments have not only increased fatigue resistance but also an anistropic flexural rigidity such that a tire incorporating them exhibit a minimum of deflection against vertically applied load and increased resistance to torsion at cornering, thus contributing to comfortable, stable drive performance. Cross-sectionally flat monofilaments when coated with rubber to produce carcass sheets may be oriented flatwise along the plane of the carcass so as to reduce the thickness of the carcass wall and further the overall weight of the tire. While flat monofilaments have such significant advantages, they are susceptible to rupture or separation at their interface with coating rubber as stresses become concentrated around sharply defined corners of the transverse cross-sectional zone of the monofilaments. This poses a durability problem with pneumatic tires in addition to reduced mechanical bond of the monofilaments with rubber as they are flat and smooth compared to multifilaments.